run-tests.py: fix diff output when test-foo.out doesn't exist.
Previously, if test-foo.out doesn't exist and test-foo outputs
something, the first line of the diff will look like this:
-+changeset: 0:
0acdaf898367
(note the leading "-")
Allow tests that end in .py and .bat
Revision
6ed46bad9530 disallowed tests that have a '.' in the name, but
that also disallows tests that end in .py and .bat, even though run-tests.py
has some code to special case them.